This invention relates to milling of materials and more particularly to systems including magnetic drives for milling materials and methods of use of the same.
In U.S. Letters Pat. No. 5,518,187, which is assigned to the same assignee as this invention and whose disclosure is incorporated by reference herein, there is disclosed a method of preparing particles of a drug or a diagnostic agent material. The method entails grinding the material in the presence of a grinding media, e.g., particles of a polymeric resin or ceramic. The polymeric resin grinding media can have a density from 0.8 to 3.0 g/cm.sup.3. and can range in size from about 0.1 to 3 mm. For fine grinding, the grinding media particles preferably are from 0.2 to 2 mm, more preferably, 0.25 to 1 mm in size. Alternatively, the grinding media can comprise particles comprising a core having a coating of the polymeric resin adhered thereon.
In U.S. Letters Pat. No. 5,862,999, which is assigned to the same assignee as this invention and whose disclosure is incorporated by reference herein, there is disclosed a method of preparing submicron particles of a therapeutic or diagnostic agent which comprises grinding the agent in the presence of grinding media having a mean particle size of less than about 75 microns. In a preferred embodiment, the grinding media is a polymeric resin. The method provides extremely fine particles, e.g., less than 100 nanometers in size, free of unacceptable contamination.
Agitator mills are known in the patent literature and are commercially available for effecting the milling of drugs, pharmaceuticals and the like. See for example U.S. Letters Pat. No. 4,620,673 (Canepa). In traditional prior art mills an agitator shaft is connected through some means to a motor. The agitator shaft is coupled at one point to a milling head and at another point to the motor. In order to keep the milled product from leaking in the area wherein the drive shaft extends into the mixing chamber, seals of some type, e.g., lip seals or mechanical seals, are used. As is known, lip seals have a rather short life span. Moreover, mechanical seals are somewhat unpredictable insofar as leakage rates and life spans are concerned. Further still, mechanical seals need a lubricant, which is typically purified water for pharmaceutical applications, thereby increasing the complexity of the structure and increasing the risk of contamination of the preparation.
Magnetically coupled mixers and pumps are commercially available for effecting the mixing or pumping of various materials. Examples of such devices are those offered by Magna-Safe International, Inc. of Woodbridge, N.J., under the Trademark MAGNASAFE.
While magnetically coupled mixers and pumps have been used previously for mixing operations, they have not been used or constructed for the production of small particle dispersions, such as the type now being utilized in the pharmaceutical, imaging, electronics and other fields. Thus, need presently exists for a magnetically coupled media milling machine for the production of small particle dispersions wherein a chamber or vessel containing the milling media and the material to be milled are located separately and without contact to the driving means that provides the grinding force. Moreover, there is a need for a magnetically coupled media milling machine for the production of small particle dispersions wherein a chamber or vessel containing the milling media and the material to be milled can be removed as an assembly after processing.
A system and method for milling at least one material. The system comprises a milling apparatus and at least one milling medium for use with the apparatus.
The apparatus comprises a milling chamber, a milling head, and a drive member. The milling chamber comprises a hollow vessel for receipt of the at least one material and the at least one milling medium therein. The drive member includes at least one drive magnet. The milling head is located within the milling chamber and is rotatably mounted with respect thereto. The milling head includes at least one driven magnet. The at least one drive magnet is magnetically coupled to the at least one driven magnet. The drive member is arranged to be rotated by an energy source, e.g., an electric motor, whereupon rotation of the drive member effects the concomitant rotation of the milling head with respect to the milling chamber. The milling head cooperates with the milling medium and with the at least one material to effect the milling of the at least one material within the milling chamber.
In accordance with one exemplary embodiment of the invention the drive member comprises an elongated drive shaft having a first end portion and a longitudinal axis. The at least one drive magnet is coupled, e.g., mounted, to the drive shaft at the first end portion. The milling head has a central bore. The milling chamber includes a spindle having a well in it. The spindle of the milling chamber is located in the central bore of the milling head but spaced slightly therefrom. The at least one driven magnet is located in the milling head adjacent the central bore. The at least one drive magnet is magnetically coupled to the at least one driven magnet via the spindle. The drive shaft is arranged to be rotated about the longitudinal axis by the energy source, whereupon rotation of the drive shaft about the longitudinal axis effects the concomitant rotation of the milling head about that axis. The milling chamber is removably mounted with respect to the drive shaft so that it can removed as a unit from the drive shaft. A removable cover is provided for the milling chamber.